"The Margonites have hunted my brethren like animals. No matter how hard we fought back, eventually we fell. They allow me to live, only to mock my suffering. Pay them back for the deaths of my brothers and I will reward you."

Accept: "I'll teach them a lesson they won't soon forget."

Reject: "You make a great pet."

When asked about quest: "Go, find the Margonites. Bring them pain and vengeance for each of the Forgotten they mercilessly hunted down."

Reward Dialogue

"I am in your debt, <name>. The Margonites may not be defeated, but at least my brethren's deaths have been avenged. Their souls are free."

Walkthrough

Just a matter of killing the forty Margonites, you can either carry on with the story (you'll reach the target soon enough), or if you want to do it quickly, you can go hunting (entering the Jennur's Horde mission is possibly the fastest place if you do not have access to the Realm of Torment yet).